When bend-forming a window glass for an automobile, at least one glass sheet cut into a predetermined size and shape is placed on a ring-like bending mold, and is stayed in a plurality of heating sections for a predetermined time in a bending zone of a heating furnace, and is conveyed into the next heating section in order, and is heated to a bending temperature (usually about 550 to 650° C.) of at least one glass sheet. Thus, the glass sheet is bended in accordance with the shape of the bending mold by self-weight.
In such a bending process of at least one glass sheet, it is necessary for obtaining a desired shape to accurately control a temperature distribution of the glass sheet at a high reproducibility. When at least one glass sheet is bended under a uniform temperature condition by placing on a ring-like bending mold, it is known that the central part of the glass sheet between frame parts at both ends of the bending mold sags and the sectional shape of the central line of the glass sheet becomes a flat pan bottom shape at the sagged part, or becomes a shape, the central part of which is somewhat lifted. In order to make a shape of aimed design, it is necessary to maintain the peripheral zone of the glass sheet at a low temperature and the central part of the glass sheet at a high temperature, thereby forming a trapezoidal temperature distribution.
In a bending process of a glass sheet, it is known to form a temperature distribution on a glass sheet. For example, it is known to employ a method of placing a locally heating device faced to the side portions of a glass sheet in order to locally largely bend the side portions of the glass sheet. However, to locally heat the side portions of a glass sheet is a technical idea different from locally heating the central portion other than deformed portions in order to prevent deformation of the peripheral portion of the glass sheet.
On the other hand, there is known a glass molding apparatus provided with a heat-shielding plate to shield a bending mold for placing at least one glass sheet from heat in order to obtain such a temperature distribution as to make the temperature of the central part higher than the temperature on both ends of the glass sheet as mentioned above.